Self-piercing rivets are used to join planar portions of workpieces together, typically two aluminum workpieces. The self-piercing rivet has a pre-formed head and a shank extending from the head. A diameter of the head is larger than a diameter of the shank. The workpieces may for example be parts of an assembly, such as parts of a vehicle, that are being secured together by riveting. In this regard, a first one of the workpieces may be secured in the assembly and the other one of the workpieces is being secured in the assembly by riveting it to the first workpiece.
Robot carried self-piercing rivet guns are often used to apply the self-piercing rivet to the workpieces. FIG. 1 is a simplified drawing of a typical robot carried self-piercing rivet gun system 100. The self-piercing rivet gun system 100 has a robotic arm 102 to which a C-shaped arm 104 is affixed. The C-shaped arm 104 has opposed ends 106, 108 with a self-piercing rivet gun 110 affixed at end 106 and the other opposed end 108 having a receptacle 112 in which an upsetting die 114 is receivable. A self-piercing rivet (not shown) having a pre-formed head is fed into self-piercing rivet gun 110 and held therein. Robotic arm 102 moves the C-shaped arm so that workpieces 200, 202 (FIG. 2) to be riveted together are between the ends of the C-shaped arm. The robotic arm 102 moves the C-shaped arm 104 to bring the upsetting die 114 against a side of workpiece 200. The self-piercing rivet gun is activated to punch a shank of the self-piercing rivet through the workpieces 200, 202. An end of the shank is deformed by a forming recess 206 (FIG. 2) in an end surface 116 of the upsetting die 114 to form the end of the shank of the self-piercing rivet into an end head having a diameter that is larger than a diameter of the shank. The workpieces 200, 202 are compressed between the pre-formed head of the self-piercing rivet and the formed end head at the end of the shank which holds the workpieces 200, 202 together. The workpiece 200 that the upsetting contacts is fixed in location with respect to the robot carried self-piercing rivet gun assembly and is referred to herein as fixedly located workpiece 200. Fixedly located workpiece 200 is typically part of an assembly, such as a part of a vehicle assembly, and the other workpiece 202 is a part that is being affixed to the fixedly located workpiece 200 and that is held in place against the fixedly located workpiece 200, such as by clamping, during riveting.
It is important that the workpieces 200, 202 are normal (perpendicular) to the self-piercing rivet gun 110, and thus the rivet, when they are riveted together. Otherwise, the integrity of the riveted joint may be compromised if the rivet extends through the workpieces 200, 202 at an angle other than ninety degrees rather than perpendicular to the workpieces.
During set-up of the robotic carried self-piercing rivet gun system 100, the robotic arm 102 is programmed so that the workpieces 200, 202 will be normal to the self-piercing rivet gun 110 during riveting. This is often accomplished by controlling the robotic arm 102 to move C-shaped arm 104 to bring the upsetting die against the fixedly located workpiece 200 that the upsetting die 114 contacts and controlling the robotic arm 102 to adjust the orientation of the C-shaped arm 104 so that the fixedly located workpiece 200 lays flat against the end surface 116 of the upsetting die 114. Thus, when the C-shaped arm 104 is moved by the robotic arm 102 to bring the upsetting die 114 against the fixedly located workpiece 200, the fixedly located workpiece 200 lies flat against the end surface 116 of the upsetting die 114 and the fixedly located workpiece 200 is thus normal to the self-piercing rivet gun 110 during riveting.
The determination of whether the workpieces 200, 202 are normal to the self-piercing rivet gun 110 is typically done manually such as by a set-up operator using devices such as machine squares and the like. Whether the robotic arm is programmed properly so that the workpieces are normal to the self-piercing rivet gun 110 is thus dependent on the subjective judgment of the set-up operator, which could lead to the robotic arm 102 being programmed so that the workpieces 200, 202 are not normal to the self-piercing rivet gun 110 during riveting.
It is thus an objective of the present invention to provide an indicator that indicates whether the workpieces that are to be riveted are normal to the upsetting die during programming of the robotic self-piercing rivet gun to minimize or eliminate subjectivity in the programming of the robotic self-piercing rivet gun.